The present invention relates to prehension units provided with optical sensors for detecting objects to be seized, as well as position controlled manipulator apparatuses including such units. The invention is particularly suitable for use in robotics, remote control and construction of motorized prothesis.
Prehension by mechanical units requires detection of the objects to be seized or gripped when the unit is closed to the object. An information almost equivalent to tactile sensation is necessary and makes it necessary to sense torques and/or forces applied to the unit. Since such units are often times used in hostile environment, the design should also be such as to avoid the detrimental effects of high temperatures, vibrations, stresses and contamination on the sensors.
Numerous attempts have been made to overcome that problem. A manipulator including means for sensing torques about three orthogonal axis and forces along said axes is shown, for example, in U.S. Pat. No. 3,952,880 (Hill et al). It includes a plurality of sensing units each having a light source, such as a LED, and a light responsive element, such as a photocell or phototransistor. The amount of light received by the light responsive element changes when there is relative movement between two components of the manipulator coupled by resilient means, caused by a force or torque to be detected.
In that arrangement, the sensors are protected against outside contamination. On the other hand, such a construction has a number of shortcomings. The light emitting and light sensitive components are located close to the object to be gripped in the manipulator. In a number of situations, they are consequently subjected to hostile conditions, such as high temperatures and vibrations. It is well known that such electronic components are frequently detrimentally affected by such conditions. Since the active sensors are distributed within the manipulator, access thereto for replacement is frequently rather difficult and time consuming.
It is an object of the invention to provide an improved prehension unit having means for sensing torque and/or forces which is particularly adapted for use under the adverse conditions encountered in practice.
It is another object to provide a prehension unit whose transducers are not subjected to the environment in which said unit may be used.
For that purpose, the invention includes a prehension unit having a supporting body, a contact element carried by the supporting body through resilient means and defining with said body a closed space and optical sensor means. Said optical sensor means comprises optical fiber means for transmitting light from a remote transducer to an end portion of said optical fiber means terminating in said supporting body in front of a locally reflecting surface of the contact element transverse to longitudinal axis of said body and optical fiber means for collecting the light reflected by said surface and conveying it to said remote receiving transducer, whereby the movements of said locally reflecting surface which result in a change of the collected amount of light may be detected.
Due to the optical fiber means, the information sensing function is completely separated in space from information processing. The transducers which cooperate in the latter function may be located together at a distance from the unit in a common housing which is not subjected to the environment of the prehension unit.
The body typically has several sensors cooperating with the contact element for detecting movements along several directions and/or tilting movements. Each sensor preferably has two optical fibers in a common terminal which confronts the locally reflecting surface.
The invention will be better understood from a consideration of the following description of particular embodiments of the invention, given by way of examples only.